Non-invasive determination of effective pulmonary blood flow: evaluation of a simplified rebreathing method.

Primary Objective: To evaluate a new technical approach to measuring effective pulmonary blood flow (PBF) in mechanically ventilated patients.

Research Design: Prospective clinical study; evaluation of accuracy and reproducibility.

Methods: Effective pulmonary blood flow was determined non-invasively in 32 mechanically ventilated patients by using a new rebreathing system (PBF(rb)). Cardiac output corrected for intrapulmonary shunt was taken as reference value (PBF(thd)). Bias, precision and reproducibility of the rebreathing method were calculated from duplicate measurements in each patient.

Main Results: The mean difference between PBF(rb) and PBF(thd) was - 0.67 +/- 0.83 l min(-1). The mean difference between duplicate measurements with the rebreathing system was 0.16 +/- 0.36 l min(-1). However, the accuracy of the rebreathing system tended to decrease in patients with PBF levels greater than 6 l min(-1).

Conclusions: The new device appears to be reliable for determination of PBF values below 6 l min(-1). With this limitation, the present method may be used as a trend-indicator of PBF in mechanically ventilated patients.